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The Defense Department has ordered an end to on-base sales of a number of workout supplements popular with military fitness buffs, concerned about potentially serious side effects of a key ingredient, DMAA. More than a dozen products containing DMAA have been yanked from on-base stores.

Originally sold as a nasal decongestant, DMAA is listed on ingredient labels as 1,3-dimethylamylamine or geranium extract, according to supplement retailer GNC. DMAA is marketed as everything from an energy enhancer to a weight-loss wonder. However, the military worries the substance may have contributed to the deaths of two soldiers who had heart attacks during physical training after using DMAA products, as well as the cases of three soldiers and two Marines who collapsed during heavy exercise.

The products were pulled pending review of any potentially serious side effects. The review won't be complete until at least late March. Officials did not ban troops from using the products.

Citing privacy concerns, the military has not released the troops' names, what products they were using, how much they had taken or other factors that may have contributed to the incidents.

"These products are legal substances and, as yet, no link between DMAA and the medical conditions reported by military medical providers has been validated scientifically by us," said Defense Department spokesman Peter Graves. "DoD has asked that the products be pulled from the shelves as a precautionary measure."

Pointing to the military's recent actions, San Bernardino, Calif., resident Johnnie Pacheco filed a class-action lawsuit against supplement maker USPlabs in U.S. District Court on Dec. 19. Pacheco contends in court filings that the company is making false and misleading statements in its marketing of DMAA supplements Jack3d and OxyElite Pro.

"The form of DMAA [USPlabs] sells in the products is a synthetic form that is both illegal and dangerous," reads Pacheco's complaint, which does not indicate that Pacheco was harmed taking the product nor that he is associated with the military.

Neither Pacheco nor his attorneys could be reached for comment by press time.

USPlabs officials declined to comment on the case or whether they had any reason to believe either of the two soldiers who died had been using their products.

"All I can say at this time is that we stand by the safety of our products," said USPlabs spokesman Jack Deschauer.

Company officials point to five peer-reviewed studies recently published by the University of Memphis in Tennessee vouching for DMAA's safety.

"Clearly, there is no cause-and-effect data" linking DMAA with any health problems, said Dr. Richard Bloomer, head of the university's Health Sport Sciences department, who helped lead the studies and consulted for Army health experts on the effects of DMAA. "I think the problem with any of these supplements is that you get [people] using doses that far exceed the typical recommendations."

DMAA was placed on the U.S. Anti-Doping Agency's banned list in August, but products with the ingredient remain legal.

Funded in part by USPlabs, Bloomer's studies showed that DMAA provided "about the same blood pressure response as two or three cups of coffee."

"I'm not a huge fan of stimulants," he said. "But the reality is that thousands of people do use them. People just need to be responsible. When they're overweight, hypertensive, exercising excessively when they're not really conditioned to do so — that's just a recipe for disaster."

Dr. William Obermeyer, head of research for the independent supplement watchdog Consumer Lab, said "a lot of these pre-workout boosters," including DMAA, are amphetaminelike compounds that work similarly to ephedrine, "but just not as strong."

DMAA is known to causes false positives for methamphetamine use on drug tests, but military officials insist follow-up testing prevents the false positives from incriminating service members.

Military leaders are taking a better-safe-than-sorry approach.

"There have been findings that this particular ingredient caused serious changes in individuals such as blood pressure, headaches, lightheadedness, stroke, depression, irregular heartbeat, dehydration, tremors and lethal exhaustion," according to a Navy announcement.

A 22-year-old soldier died after collapsing during a unit run on a base in the Southwest this summer, said Maria Tolleson, a spokeswoman for the Army surgeon general. This fall, a 32-year-old at the same base collapsed after a PT test, then died after a month in the hospital.

GNC spokesman Greg Miller said the company has sold 440 million doses of DMAA products since 2007, with only one report of any problems.